Episcopal priest the Rev. Albert Cutie will attend Trinity Cathedral in downtown Miami with virtually all Christian denominations as well as Imams and Rabbis in attendance. [Editor's note: The original version misstated Father Cutie's religion.]

University of Minnesota’s Nick Campbell, who calls himself a “non-denominational Christian,” will likely be “too caught up in my own schedule, agenda, schooling, etc…. too distracted to pray … something I am always working on.”

The common denominator is that all of the above consider themselves highly religious people who heartily welcome today’s National Day of Prayer, a day formally designated by Congress and President Harry Truman in 1952 and carried on by every president since. Similar proclamations were signed last year by all 50 state governors and those of several US territories.

“I think this day is a huge deal and very important for a nation like ours based on Judeo-Christian principles to really reflect,” says Father Cutie, author of “Dilemma: A Priest’s Struggle with Faith and Love." “This is not just a way of dealing with news on the economy and terrorism but to teach future generations long term to put their trust in a higher power, no matter what they consider that to mean.” [Editor's note: The original version misstated the name of Father Cutie's book.]

Separation of church and state?

That comment makes some people – atheists and civil libertarians – uncomfortable with what they feel is the day’s foggy blend of patriotism and religion. For others, it seems to be a clear violation of America’s constitutional separation of church and state. But legal analysts say the proclamation passes legal muster because it does not force people to pray on this day.

“From a constitutional perspective, there is nothing infirm about a National Day of Prayer,” says Harold Krent, a professor at Chicago-Kent College of Law. “Congress has not thereby established a religion, nor has it infringed anyone’s right to follow the dictates of his or her own religion.”

That said, the day could be applied in an unconstitutional manner, he says.

“For instance, school districts requiring prayer on a National Day of Prayer would, in all likelihood, violate the Establishment Clause. Schools can study about prayer and the role of prayer in our lives, but not require or even strongly encourage prayer, particularly in younger grades," says Professor Kent. "Conversely, however, governors and the president can encourage us to pray in our private lives, without establishing a religion or coercing religious practices.”

Such observances will go on in dozens of forms – from long speeches to short notices to silent prayers sponsored by congregations small and large.

“This is a very positive thing and the more of it and the more diverse, the better,” says author and television personality Rabbi Shmuley Boteach. “Unlike Europe, where such a day would be impossible, this is what makes the US the multiple and varied society that it is. We are all Americans and pray to the same God. This spotlights the collective and raises us all above our denominations to realize we are all one, human family.”

The origin of the day goes back to the Founding Fathers.

The Continental Congress asked the colonies to pray for wisdom in forming a nation in 1775, and Thomas Jefferson said in 1808: “Fasting and prayer are religious exercises; the enjoining them an act of discipline. Every religious society has a right to determine for itself the time for these exercises, and the objects proper for them, according to their own particular tenets; and right can never be safer than in their hands, where the Constitution has deposited it.”

Abraham Lincoln, in the midst of the Civil War proclaimed a day of “humiliation, fasting, and prayer” in 1863. Ninety years later, Congress passed a formal declaration marking an annual event on the first Thursday of May and Harry Truman signed it into law.

Muslim participation

“Muslims already pray by themselves five times a day,” says Mr. Ali, director of Project Islamic HOPE (Helping Oppressed People Everywhere), an advocacy organization in Los Angeles. “What makes this different for us is that we can build solidarity with other faiths.”

He says he is looking forward to the mosque's Imam making it clear that Al Qaeda has a terrorist ideology which most mainstream Muslim organizations don’t share. “This is both personal and private as well as public and collective," says Ali. "Bin Laden's capture was the answer to our prayers so we will be giving thanks for that as well."

"The National day of prayer, although historically significant, has generally been organized and observed by Christian denominations," she says. "We hope to see this annual day of prayer become more inclusive of all faith traditions. This year in particular, we call on all Americans to pray for the victims of injustices, terror and oppression in America and around the world, for our nation to be healed and strengthened, and for our troops to be brought back home soon."

How presidents have observed it

On his first National Day of Prayer as President in 2009, President Obama distanced himself from the National Day of Prayer by foregoing a formal early morning service and not attending a large Catholic prayer breakfast the next morning. Then-White House Press Secretary Robert Gibbs said Obama was reverting back to pre-Bush presidential practice.

The day is not without its controversies.

Rabbi Boteach says that several years ago, two Jewish rabbis took offense when one White House prayer breakfast focused directly on Jesus. “The rabbis asked, ‘How could this be a national day of prayer?’ " he says, noting that the Jewish community often doesn’t participate as much as he would like.

“But I disagreed with them, saying that every Christian has a right to pray to Jesus," he says. "This day doesn’t necessarily mean we all brush aside our spiritual techniques in order to be more universal – just that we should all not overdo it. I think this day needs more attention. I salute the idea completely.”